Effective Surface Recombination of p+ Layers Doped Using Ion Implantation or Surface Deposited B Sources

Two key factors need to be fulfilled in order to enable high efficiency bifacial p-type PERT cell. High bulk lifetime values retention during production processes, and minimized effective surface recombination, Seff in the p+ layer. The influence of boron doped layer parameters on the effective surface recombination in the p+ layer of an n+-p-p+ bifacial PERT solar cell is evaluated. Back IQE data of n+-p-p+ cells with over-doped p+ layer were used for evaluation of Seff values in the p+ layer. Simulation was made for several doping profiles with the surface doping concentration, Bs, in the range 1018 - 1020 cm-3. According to simulation, the dominating parameter controlling the effect of the built-in charge in the passivation layer on the effective surface recombination is the Bs level. For Bs values above ∼1019 cm-3 this charge has no significant influence. p+ layer doping was made by B ion implantation as well as by thermal diffusion from deposited B source. Measurements were performed on symmetrically B doped n-Si wafers with different passivation. Good agreement between simulation and measurements was found.